Field of the Invention and Related Art Statement
This invention relates to an apparatus for marking a high point mark on a sidewall of a tire at a peak position of a primary waveform of a radial force variation (RFV) of the tire.
In order to make performance of tires high, a tire uniformity has to be improved. As one of the means for improving this tire uniformity, it is effective to buff the tire selectively to decrease the RFV of the tire, which means the peak-peak value of the variation of the radial force of tire during one complete rotation of tire.
However, radial runout is generally generated on a bead seat of wheel. Thus, there is an effective method to improve the RFV of tire as a whole which is to make the bottom of valley of the primary waveform of the radial runout of the wheel coincident with the peak point of the primary waveform of RFV of the tire, which was measured by setting the relevant tire on a standard rim having a radial runout preciously decreased. For the sake of making such improvement on the tire, it is necessary to detect the peak position of the primary waveform of RFV of the tire and a high point mark should be recorded upon said peak position, for example, by thermoprinting. Therefore, the conventional marking apparatus for tires has been designed such that a rotating amount of an electric motor for rotating a spindle on which a standard rim is arranged is controlled so that the peak position of RFV of the tire is stopped at the predetermined marking position.
FIG. 1 is a graph showing a manner of controlling rotating velocity of an electric motor in the conventional marking apparatus. As shown in FIG. 1, the tire is rotated at a constant velocity V.sub.0 until the time t.sub.1. The peak position of RFV of the tire forms a predetermined angle with the marking point at the time t.sub.1. Thereafter, the rotating velocity of the tire is gradually decreased until the time t.sub.2 and then remains at a constant lower velocity V.sub.L until the time t.sub.3. After the time t.sub.3, the rotating velocity of the tire is gradually decreased again and the tire is stopped at the time of t.sub.4.
In the above-mentioned conventional method for controlling the rotating amount of the electric motor, the rotation of tire is controlled from the instant t.sub.1 that the peak point of RFV of the tire comes to the position forming a predetermined angle with the marking position until the time t.sub.4 that the peak point of RFV of the tire comes at the marking position That is to say, just after the time t.sub.1, the rotating velocity of tire is reduced to the lower velocity VL and the final reduction of the rotating velocity starts from the time t.sub.3. Therefore, the tire rotates at the lower velocity for 3.about.5 seconds on average, and the processing time for marking is so long and the processing efficiency is low.
It can be considered to make the lower rotating velocity V.sub.L higher in order to shorten the processing time per one tire. But, in this case, it will be difficult to stop the tire at the desired position in a precise manner. Further, if the tire runs over the desired position, it would be necessary to rotate the tire in the reverse direction, as a result, the whole time for processing might becomes too long.
Furthermore, in the conventional marking apparatus for tires, the rotating velocity of tires is controlled with the aid of pulses each of which is derived when the tire is rotated over an angle of 360/128, i.e. 2.8.degree.. Thus, there is a disadvantage that the tire stops at the desired position with only the precision of 2.8.degree.. This precision is too low to effect the desired control.